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991.
Basing on the simulation results, it is shown that the Townsend mechanism of electron multiplication in a gas at sufficiently
large interelectrode distances is valid at least up to such large values of E/p at which relativistic electrons are generated.
Correspondingly, the runaway electron producing in a gas is determined not by the local criteria accepted presently, but by
the ratio of interelectrode distance and the characteristic electron multiplication length. It is shown that the critical
discharge voltage U, at which the runaway electrons appear in a given gas, is a function of the product of the interelectrode
distance by the gas pressure. This function (U-pd dependence) defines not only well-known Paschen curve but also an additional branch, which describes the absence of a self-sustained
discharge at a high voltages sufficiently rapidly supplied across the electrodes. Critical discharge voltage dependence for
helium and xenon are presented. 相似文献
992.
993.
994.
Kernel type density estimators are studied for random fields. It is proved that the estimators are asymptotically normal if
the set of locations of observations become more and more dense in an increasing sequence of domains. It turns out that in
our setting the covariance structure of the limiting normal distribution can be a combination of those of the continuous parameter
and the discrete parameter cases. The proof is based on a new central limit theorem for α-mixing random fields. Simulation
results support our theorems.
Final version 29 October 2004 相似文献
995.
Given an integer k>0, our main result states that the sequence of orders of the groups (respectively, of the groups ) is Cesàro equivalent as n→∞ to the sequence C1(k)nk2?1 (respectively, C2(k)nk2), where the coefficients C1(k) and C2(k) depend only on k; we give explicit formulas for C1(k) and C2(k). This result generalizes the theorem (which was first published by I. Schoenberg) that says that the Euler function ?(n) is Cesàro equivalent to . We present some experimental facts related to the main result. To cite this article: A.G. Gorinov, S.V. Shadchin, C. R. Acad. Sci. Paris, Ser. I 337 (2003). 相似文献
996.
997.
Yury Kostyukevich Alexey Kononikhin Igor Popov Eugene Nikolaev 《Journal of mass spectrometry : JMS》2014,49(10):989-994
In the paper, we have demonstrated the possibility of performing hydrogen/deuterium (H/D) exchange of proteins in the region of gas‐phase ion formation in an electrospray ion source by saturating the electrospray ionization source with vapors of a deuterating agent (D2O or MeOD). In this region, charged droplets are shrinking and the protein ions transfer into the gas phase. As a model protein, we have used ubiquitin whose ion mobility spectrometry and gas‐phase H/D exchange in the vacuum part of a mass spectrometer demonstrated the presence of gas‐phase conformers with different cross sections and H/D exchange rates. In our experiments, we observed monomodal deuterium distributions for all solvents, charge states, desolvating capillary temperature and types of deuterating agent. Also, we found that the number of H/D exchanges increases with an increasing desolvating capillary temperature and decreasing charge state. We observed that solution composition (49 : 50 : 1 H2O : MeOH : formic acid or 99 : 1 H2O : formic acid) influences the charge‐state distribution but did not change the degree of H/D exchange for the same charge state. Electron‐capture dissociation fragmentation shows that higher charge states contain a segment that is protected from access by the deuterating agent. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
998.
Alexey I. Baranov 《Journal of computational chemistry》2014,35(7):565-585
For the fully relativistic 4‐component many‐electron wavefunction six flavors of electron localizability indicators (ELI) have been proposed. Their counterparts, suitable for the application to the 2‐component wavefunctions, have been also derived. Six proposed indicators have been tested on Ar and Rn atoms and one of them, the ELI‐D for spatially antisymmetrized electron pairs, has been found to reveal atomic shell structures at quantitative level. Shell structures of all the atoms of periods 4–7 of the periodic table have been obtained using this indicator and compared with these obtained from the nonrelativistic limit calculations as well as from scalar‐relativistic (zero‐order regular approximation) calculations. © 2014 Wiley Periodicals, Inc. 相似文献
999.
Ji Ma Yubin Fu Dr. Evgenia Dmitrieva Dr. Fupin Liu Dr. Hartmut Komber Dr. Felix Hennersdorf Dr. Alexey A. Popov Prof. Dr. Jan J. Weigand Dr. Junzhi Liu Prof. Dr. Xinliang Feng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(14):5686-5691
Three unprecedented helical nanographenes ( 1 , 2 , and 3 ) containing an azulene unit are synthesized. The resultant helical structures are unambiguously confirmed by X-ray crystallographic analysis. The embedded azulene unit in 2 possesses a record-high twisting degree (16.1°) as a result of the contiguous steric repulsion at the helical inner rim. Structural analysis in combination with theoretical calculations reveals that these helical nanographenes manifest a global aromatic structure, while the inner azulene unit exhibits weak antiaromatic character. Furthermore, UV/Vis-spectral measurements reveal that superhelicenes 2 and 3 possess narrow energy gaps ( 2 : 1.88 eV; 3 : 2.03 eV), as corroborated by cyclic voltammetry and supported by density functional theory (DFT) calculations. The stable oxidized and reduced states of 2 and 3 are characterized by in-situ EPR/Vis–NIR spectroelectrochemistry. Our study provides a novel synthetic strategy for helical nanographenes containing azulene units as well as their associated structures and physical properties. 相似文献
1000.
Alexey Voronov Atsushi Urakawa Wouter van Beek Nikolaos E. Tsakoumis Hermann Emerich Magnus Rønning 《Analytica chimica acta》2014
Large datasets containing many spectra commonly associated with in situ or operando experiments call for new data treatment strategies as conventional scan by scan data analysis methods have become a time-consuming bottleneck. Several convenient automated data processing procedures like least square fitting of reference spectra exist but are based on assumptions. Here we present the application of multivariate curve resolution (MCR) as a blind-source separation method to efficiently process a large data set of an in situ X-ray absorption spectroscopy experiment where the sample undergoes a periodic concentration perturbation. MCR was applied to data from a reversible reduction–oxidation reaction of a rhenium promoted cobalt Fischer–Tropsch synthesis catalyst. The MCR algorithm was capable of extracting in a highly automated manner the component spectra with a different kinetic evolution together with their respective concentration profiles without the use of reference spectra. The modulative nature of our experiments allows for averaging of a number of identical periods and hence an increase in the signal to noise ratio (S/N) which is efficiently exploited by MCR. The practical and added value of the approach in extracting information from large and complex datasets, typical for in situ and operando studies, is highlighted. 相似文献